问题 解答题
正项数列{an}满足
a2n
-(2n-1)an-2n=0.
(1)求数列{an}的通项公式an
(2)令bn=
1
(n+1)an
,求数列{bn}的前n项和Tn
答案

(1)由正项数列{an}满足:

a2n
-(2n-1)an-2n=0,

可得(an-2n)(an+1)=0

所以an=2n.

(2)因为an=2n,bn=

1
(n+1)an

所以bn=

1
(n+1)an

=

1
2n(n+1)

=

1
2
(
1
n
-
1
n+1
),

Tn=

1
2
(1-
1
2
+
1
2
-
1
3
+…+
1
n
-
1
n+1
)

=

1
2
(1-
1
n+1
)

=

n
2n+2

数列{bn}的前n项和Tn

n
2n+2

单项选择题 A1/A2型题
单项选择题